1. Field of the Invention
The present invention relates to a color image display apparatus.
2. Description of the Prior Art
FIGS. 1 and 2 show examples of prior art color image display apparatus of high resolution type. In these drawings, REA (in FIG. 2), REAr (red), REAg (green) and REAb (blue) (in FIG. 1) denote light emitting element arrays, respectively, each of which is formed by arranging a great number of light emitting elements (e.g., light emitting diodes) in a straight line. Further, CSA denotes a three-color resolving (or synthesizing) optical system composed of prisms Pr and Pb, a dichroic prism DP, reflection surfaces Mr and Mb, etc.
In the display apparatus shown in FIG. 1, three light emitting element arrays REAr, REAg and REAb are arranged in parallel to each other in a space. Three sorts of light beams (three primary colors) emitted from these three regions independently are focused on three spacial light modulation elements (SLMr, SLMg and SLMb) through three focusing lenses Lr, Lg and Lb end three light deflection elements DMgr, DMg end DMb, respectively.
In the display apparatus shown in FIG. 2, on the other hand, one light emitting element array REA is divided into three regions of r(red), g(green) and b (blue) arranged in series. Three sorts of light beams (three primary colors) emitted from these three regions are focused on three spacial light modulation elements (SLMr, SLMg and SLMb), respectively through a single focusing lens L and a single light deflection element Mg.
Further, in both FIGS. 1 and 2, a read light emitted from a read light source LS is written in the three spacial light modulation elements SLMr, SLMg and SLMb, respectively through a polarizing light beam splitter PBS and a three-color resolving (or synthesizing) optical system, to read three different optical information from the three spacial light modulation elements SLMr, SLMg and SLMb, separately. The three sorts (primary colors) of optical information read from the three spacial light modulation elements SLMr, SLMg and SLMb, separately are synthesized (or resolved) by the three-color resolving (or synthesizing) optical system CSA, introduced to a projection lens Lp through the polarizing light beam splitter PBS, and then projected upon a screens through the projection lens Lp as a color image.
In the display apparatus, N-units of light beams emitted from the N-unit light emitting elements of the light emitting arrays, respectively are introduced to the three light deflection elements DMr, DMg, DMb through the focusing lenses Lr, Lg and Lb, respectively in FIG. 1, and to the light deflection element Mg through the focusing lens L in FIG. 2 under such conditions that the intensities of these three light beams are modulated (referred to as intensity-modulated, hereinafter) on the basis of N-units of pixel information. Further, the deflected three light beams are focused on three photo-conductive layer members of the three spacial light modulation elements (SLMr, SLMg and SLMb), respectively. Further, under these focused conditions, the three light beams are scanned repeatedly in the perpendicular direction of the three spacial light modulation elements SLMr, SLMg and SLMb, respectively, so that the three light beams are written in the three spacial light modulation elements SLMr, SLMg and SLMb, respectively.
In the following description, where a plurality of spacial light modulation elements SLM are explained, these elements SLM are distinguished from each other by attaching some suffixes to the elements SLM. However, where these elements are explained in common without any distinction, no suffix is attached to the elements. Here, the spacial light modulation element SLM is formed as shown in FIG. 3, for instance. In more detail, the spacial light modulation element SLM is formed by laminating a transparent substrate BP1, a Transparent electrode Et1, a photo-conductive layer member PCL, a dielectric mirror DML, a light modulation substance layer member PML, a transparent electrode Et2, and a transparent substrate BP2. The transparent electrodes Et1 end Et2 are of a thin film, respectively formed of a transparent photo-conductive substance. Further, the photo-conductive layer member PCL is formed of a substance having photo-conductive characteristics in a wave length band of light to be used. Further, the dielectric mirror DML is a known multilayer structure by which light of a predetermined wave length band can be reflected. Further, the light modulation substance layer member PML is formed of a light modulating substance by which light status (deflection, polarization, scattering, etc.) can be changed according to the strength of an electric field applied to the modulation substance thereof.
The above-mentioned light modulation substance is a nematic liquid crystal activated in various modes such as TN mode, hybrid field effect mode (HFE), guest host mode (GH), electric field induced double refraction mode (vertical or horizontal orientation), dynamic scattering mode, phase transition mode, etc., for instance. In particular, when the nematic liquid crystal of vertical orientation is used in the electric field induced double refraction mode, since the dependency of the light modulation effect upon the wave length of the read light can be reduced, it is possible to obtain a high contrast image. As the other light modulation substances, there are smetic liquid crystal, ferroelectric liquid crystal, etc. Further, electro-optic crystals such as lithium niobate, BSO, PLZT, etc. and high molecular-liquid crystal composite film, etc. can be used as the light modulation substance.
In FIG. 3, E denotes a power source for supplying a predetermined voltage between the two transparent electrodes Et1 and Et2. Although shown as an alternating voltage power source, this power source can be replaced with a direct current voltage power source according to the substance for constituting the light modulation substance layer member PML. Further, in FIG. 3, WL denotes a write light beam incoming to the substrate (BP1) side of the spacial light modulation element SLM and focused on the photo-conductive layer member PCL. This write light beam is intensity-modulated according to the image information to be displayed. That is, N-unite of the write light beams WL each of whose intensity is modulated according to the image (pixel) information to be displayed are introduced to the transparent substrate (Et1) side of the spacial light modulation element SLM, to which a predetermined voltage of the voltage source E is applied between the two transparent electrodes Et1 and Et2.
When the write light beam is focused upon the photo-conductive layer member PCL through the transparent substrate BP1 and the transparent electrode Et1, the electric resistance of the photo-conductive layer member PCL (at which the write light beam is focused) changes according to the quantity of the write light beam, so that an eclectic field having an electric field strength distribution corresponding to the quantity of the write light beam WL is to be applied between both ends of the light modulation substance layer member PML. The distribution of the electric field strength corresponds to the level change of the sequential pixel signals generated in time series manner.
Therefore, when the read light RL is introduced to the transparent substrate (BP2) side of the spacial light modulation element SLM, the introduced read light reaches a dielectric mirror DML by way of the transparent substrate BP2.fwdarw.the transparent electrode Et2.fwdarw.the light modulation substance layer member PML.fwdarw.the dielectric mirror DML. After that, being reflected therefrom, the reflected read light outgoes by way of the dielectric mirror DML.fwdarw.the light modulation substance layer member PML.fwdarw.the transparent electrode Et2.fwdarw.the transparent substrate BP2. The light status of the N-unit light beams outgoing from the spacial light modulation element SLM changes according to the level change of the pixel signals generated in time series manner.
Therefore, when material constituting the light modulation substance layer member PML of the spacial light modulation element SLM can change the polarization status or double refraction status of the light beam passed through the element SLM according to the electric field strength applied thereto, the polarization status or the polarization plane status of the reflected read light beam outgoing from the spacial light modulation element SLM changes according to the N-units of sequential pixel information generated in time series manner. Accordingly, when the light beam outgoing from the spacial light modulation element SLM is passed through an analyzer (or the polarizing light beam splitter PBS), it is possible to obtain the light beam whose intensity changes according to the N-units of sequential time-series pixel information.
In the above-mentioned prior art color image display apparatus as shown in FIG. 1, however, three light beams are emitted from the three light emitting element arrays REAr, REAg and REAb arranged in parallel to each other in a space. Further, these light beams are focused on the three spacial light modulation elements (SLMr, SLMg and SLMb) through three focusing lenses Lr, Lg and Lb and the three light deflection elements DMgr, DMg and DMb, independently to write the optical information in the three spacial light modulation elements (SLMr, SLMg and SLMb), separately. Accordingly, there exists a problem in that various errors are inevitably produced due to the manufacturing error of the optical lenses, the mounting error of the lenses to lens barrels, the eccentricity of the optical axes of the lenses, the error of the light deflector, etc.
Further, since the respective optical paths are provided between the three light emitting element arrays REAr, REAg and REAb and the three spacial light modulation elements (SLMr, SLMg and SLMb) respectively, the image distortions generated by the respective optical members arranged in the respective optical paths are independent from each other without any correlation between them, with the result that it is extremely difficult to superimpose a plurality of high resolution images under excellent conditions. In the case of the color image display in particular, since a plurality of optical information must be displayed simultaneously, it is impossible to display color images of high resolution.
On the other hand, in the case of the prior art color image display apparatus shown in FIG. 2, one light emitting element array PEA is divided into three regions of r, g and b being arranged in series, and three light beams are emitted in parallel individually. Further, these three sorts of light beams emitted from these three regions are focused on three spacial light modulation elements (SLMr, SLMg and SLMb), respectively through a common focusing lens L and a common light deflection element Mg. Therefore, the three sorts of light beams emitted from the three different regions r, g, and b of one light emitting element array REA in parallel to each other are introduced to the image-forming lens L at three different incident angles. Therefore, the images of the optical information emitted from three different divided regions r, g and b of the one light emitting element array REA have three different image distortions, independently. As a result, it is extremely difficult to superimpose a plurality of high resolution images under excellent conditions. In addition, there exists another problem in that MTF (mean time to failure) of the display apparatus is degraded and shear (dislocation) occurs in color image.
Further, in the prior art color display apparatus, the major light beam goes and returns in the same optical path through the color resolving or synthesizing means, with the result that there exists another problem in that the contrast is degraded and the resolution is lowered. In addition, since an expensive polarization beam splitter operative to light of a wide wave length band (white light) excellently must be used and further an expensive projection lens of long lens back is required, there arises another problem in that the display apparatus is costly.
Further, in the prior art display apparatus, since a plurality of light begone having plural optical information are synthesized into one light beam, the optical synthesizing system is relatively complicated in proportion to the number of the optical information, so that the attenuation rate of the optical information increases. In order to project a bright color image on the screen, the light emitting elements of high power type must be used under consideration of the increased attenuation rate of the optical information. In addition, in order to superimpose the plural optical information, a complicated adjusting mechanism has been so far required.